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Agh potential heating nightmare!! (PigletJohn...?)

(14 Posts)
superlambanana Fri 14-Mar-14 14:35:03

In the middle of our extension and the previous owners, with whom we are still quite friendly, popped round to see how it was getting on. I mentioned we were getting a new combi boiler as part of it to replace the current one (not a combi, is about 12yrs old). They said there might e an issue with fitting a new boiler to the current pipes (I can't remember what type of pipes they are) and that they had a few issues when putting the last one in.

Builder doesn't reckon the current boiler will cope with the bathroom, utility, kitchen and bedroom we're adding. I am now really worried we'll have to have the entire system replaced. The house was built in 1935 and the pipes to the radiators run down the inside of the downstairs rooms so are visible iyswim.

Are they right? How much would that cost?! Old bit of house is 3 bed 1 bath 2 reception rooms. Help..!!

TheGreatHunt Fri 14-Mar-14 14:45:59

Get a few quotes from plumbers you trust or are recommended. I remember when we had our boiler in they asked us if we wanted to ever put a new bathroom in and if so, we should get a better boiler. So we did. But no change to the system itself.

superlambanana Fri 14-Mar-14 14:55:01

We have a plumber - that's not the issue. I'm more concerned about whether we will have to have an entirely new system to go with the new boiler as apparently it may not be able to be put onto the old system!

MummytoMog Fri 14-Mar-14 15:02:13

Did they say exactly what the problem was? And are you moving the boiler anyway? Our old boiler had the wrong size gas supply pipe, which cost us very little to have re run when we had a new boiler. In addition, quite a bit of our old pipework was steel, so when we built our extension we had all the steel replaced (we were moving the boiler anyway) at the same time. It didn't add massively to the cost.

We had our old boiler in the garage, which was demolished, so were always going to move it into the utility room, but the easiest thing ended up to be putting it inside a cupboard in the loft en suite. We ran our supply pipes down the old side stack (copper water tank was still in there from the conventional boiler, and then under the floorboards so it's pretty neat and tidy. We also went for a slightly bigger boiler to make sure it could cope with the extra demand on it when we extended and we now slightly wish we'd gone for an even bigger one as we've added a lot of radiators!

It cost us about �3000 to put in a new boiler (Worcester Bosch Greenstar), new gas supply pipework, several new radiators and some new copper pipes to replace the old steel ones. It then cost us a further �1k to move the boiler upstairs and re run the supply pipework again (and build a little cupboard around it). I think our boiler installation was quite expensive, and if your builder can subcontract it to someone reliable and reasonable in cost, then you might well be able to manage it all more cheaply.

We also rewired while we had the floorboards up. Well worth doing, electrics were a death trap.

PigletJohn Fri 14-Mar-14 16:20:31

perhaps they mean the incoming pipe is too small and you will not get enough flow from the taps if you move to a combi. This is a very common problem, although single-occupancy homes don't notice it so much.

Fill a bucket at the kitchen cold tap, time it, calculate how many litres per minute it delivers.

You might end up needing to lay a new water pipe inside the house and all the way to the main in the pavement.

Any combi will have difficulty feeding more than one bath or shower at a time. What made you choose a combi?

It is very unusual for modern boilers to have insufficient power to heat a house, so it is only the hot water from a combi that is likely to be a problem. Modern houses usually need less than 12kW output for heating, and modern boilers are usually more than that. Builders are often quite bad at calculating heat loss. It depends how old and how big your house is, and how badly insulated.

PigletJohn Fri 14-Mar-14 16:23:24


if the radiator pipes are plastic, they might be old non-barrier pipe, which lets air diffuse in, resulting in your radiators and boiler rusting away from the inside quite quickly. If they are microbore pipes
(size of a pencil) they belong in the skip.

superlambanana Fri 14-Mar-14 17:15:13

Oh heck. I'm fairly sure the previous owner said they were microbore. sad

Think the usual width of the two pipes going into the floor either side of a radiator (ie the ones that the thermostatic valves sit on) - thy are that width all the way up.

We don't have to have a combi - I suppose we just ashamed they were better! We're planning to have an electric shower in the bathroom and a mixer in the ensuite if that makes a difference. The problem is, to have the electric shower we have to move or get rid of the hot water tank or the shower would be across the window.

PigletJohn Fri 14-Mar-14 17:18:14

do the bucket test before you commit to a combi.

Is there something wrong with the old boiler?

Microbore pipes are the size of a pencil. Ordinary copper pipes to an individual radiator are 15mm (the sixe of your finger)

superlambanana Fri 14-Mar-14 17:23:11

They look somewhere in between..! I'd say about 10mm perhaps. If they do turn out to be microbore what would the implications be? <frets about cost>

superlambanana Fri 14-Mar-14 17:26:43

Got about 11.5l in a minute from the cold tap - but I've no idea what that means!

PigletJohn Fri 14-Mar-14 18:14:07

11.5lpm is enough for an adequate shower, except when someone turns on another tap, flushes a WC, or fills a washing machine at the same time.

A bath contains about 100 litres of water so will be slow to fill if you get a combi.

Microbore systems are prone to clogging with sediment because they cannot be powerflushed. They are difficult to extend by adding new radiators. 10mm is microbore. It would be best to bin it and start again. New pipes will preferably be run under the floors (microbore is usually on show because it is a cheap option)

superlambanana Fri 14-Mar-14 19:03:09

Ugh, I was afraid you'd say that! (Thank you so much by the way - I can't tell you how helpful this is!!)

We have solid ground floors - does this mean the pipes will still have to be external? Does anyone have any idea how much replacing the lot would cost?

MummytoMog Fri 14-Mar-14 22:11:07

Solid floors? That seems unusual for a thirties house.

superlambanana Fri 14-Mar-14 23:31:24

I think lots of things about our house are unusual Mummytomog! Definitely solid floors - had to have big channels dug out all down the walls for new wiring. No cavity in the wall either. Sigh.

It's going to cost a fortune isn't it? sad

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